On Fri, Oct 09, 2015 at 12:40:21PM +0300, Andrey Ryabinin wrote: > 2015-10-09 12:10 GMT+03:00 Will Deacon <will.deacon@xxxxxxx>: > > On Fri, Oct 09, 2015 at 11:12:24AM +0300, Andrey Ryabinin wrote: > >> 2015-10-08 22:02 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>: > >> > --- a/arch/arm64/kernel/image.h > >> > +++ b/arch/arm64/kernel/image.h > >> > @@ -59,4 +59,31 @@ > >> > _kernel_offset_le = DATA_LE64(TEXT_OFFSET); \ > >> > _kernel_flags_le = DATA_LE64(__HEAD_FLAGS); > >> > > >> > +#ifdef CONFIG_EFI > >> > + > >> > +/* > >> > + * The EFI stub has its own symbol namespace prefixed by __efistub_, to > >> > + * isolate it from the kernel proper. The following symbols are legally > >> > + * accessed by the stub, so provide some aliases to make them accessible. > >> > + * Only include data symbols here, or text symbols of functions that are > >> > + * guaranteed to be safe when executed at another offset than they were > >> > + * linked at. The routines below are all implemented in assembler in a > >> > + * position independent manner > >> > + */ > >> > +__efistub_memcmp = __pi_memcmp; > >> > +__efistub_memchr = __pi_memchr; > >> > +__efistub_memcpy = __pi_memcpy; > >> > +__efistub_memmove = __pi_memmove; > >> > +__efistub_memset = __pi_memset; > >> > +__efistub_strlen = __pi_strlen; > >> > +__efistub_strcmp = __pi_strcmp; > >> > +__efistub_strncmp = __pi_strncmp; > >> > +__efistub___flush_dcache_area = __pi___flush_dcache_area; > >> > >> So why we need these __pi_* aliases? > >> We could just do __efistub_memcmp = memcmp; Right? > > > > We *could*, but that defeats the whole purpose of tagging > > position-independent functions explicitly in the kernel text. > > > > I just don't get that "the whole purpose of tagging". > > Yes, the EFI stub is allowed to call only PI kernel functions. > But the EFI stub already protected by __efistub_ namespace. > If we want to use some new PI function in the stub, we would need add > it into this list at first. > So that __pi_ namespace doesn't bring any protection or isolation. What it does it force people making future changes to the __pi_* functions to think about the stub, otherwise if the function happens to be position-independent when efistub starts using it, it could easily break due to some future patch where the author didn't realise that it was being used in that manner. Will -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
